Process for the production of plastic components for containing and/or transporting fluids

ABSTRACT

The invention provides a process for producing a component of a plastics material which is strengthened and reinforced by a resin-impregnated fibrous material which adheres to a surface thereof The surface of the component is contacted with a fibrous material impregnated with a resin in a settable state, and setting of the resin is effected, while the fibrous material is caused to adhere to the surface of the component. The plastics component is a polyolefin material, and the surface is subjected to activation by oxyfluorination thereof prior to the contacting.

FIELD OF THE INVENTION

THIS INVENTION relates to a process for the production of plasticscomponents, eg components for containing and/or transporting fluids,wherein the components are strengthened or reinforced by aresin-impregnated fibrous material. The invention also relates to suchstrengthened or reinforced components, in particular pipes and tanks,particularly when produced by means of said process.

By way of background the Applicant is aware that published JapanesePatent Application JP-A-62/070 028 discloses treatment of thermoplasticresin polyolefin, with a low temperature tetrafluorocarbon plasma. Thistreatment, however, is for the purpose of preparing the polyolefinsurface for laminating the polyolefin with a layer of thermosettingresin by heating.

SUMMARY OF THE INVENTION

According to the invention, in the production of a component of aplastics material which is strengthened and reinforced by a fibrousmaterial which has been impregnated with a resin which adheres to asurface of the component by contacting said surface of the componentwith said fibrous material impregnated with the resin in a settablestate, and effecting setting of the resin to cause saidresin-impregnated fibrous material to adhere to said surface of thecomponent, the process which comprises using as the plastics material apolyolefin material and which includes the step, prior to thecontacting, of subjecting said surface of the component to activationthereof, the activation being by surface fluorination in the form ofoxyfluorination by exposing the surface of the component to anactivating gas consisting essentially of molecules and comprisingfluorine-containing molecules and oxygen-containing molecules at apressure of 1-500 kPa, the gas being at a temperature of above 0° C.,the plastics material of the component having a melting point above saidgas temperature and the oxyfluorination acting to incorporatefluorine-containing substituents and oxygen-containing substituents,derived from the molecules of the activating gas, into the surface ofthe component.

By activation is meant that the surface of the component is brought intocontact with a fluid in a fashion whereby atoms, molecules and/orradicals derived from the fluid are incorporated into the surface of thecomponent.

The component may be tubular or hollow cylindrical, eg circular orsquare in cross-section, suitable for containing and/or transporting afluid. In particular the component may be a pipe or pipe fitting, or atank. While the polyolefin material may be any suitable hydrocarbonpolymer, typically, the polyolefin material is polyethylene (PE), eghigh density polyethylene (HDPE), polypropylene (PP), or polyolefiniccopolymers such as copolymers of ethylene and propylene, egethylene-propylene-diene monomer elastomer (EPDM), or blends of suchpolymers. Accordingly, the polyolefin material may be selected from thegroup consisting of polyethylenes, polypropylenes, copolymers ofethylene and propylene and blends of such polyolefins; and the surfaceactivation may act to provide the surface-activated component with asurface tension at 20° C. of at least 40 mN/m. The polyolefins usedinclude unmodified or modified polyolefins, eg those modified bycontaining ethyl vinyl acetate as an impact modifier.

DESCRIPTION OF THE RELATED ART

Any suitable surface fluorination technique can be used to fluorinatethe surface of the component before the fibrous material is adhesivelysecured thereto. By fluorinated is meant that the surface of the pipe ortank is treated with a fluorine-containing gas to provide fluorinesubstituents bound to said surface. Examples of suitable fluorinatingtechniques include, for example, those described in U.S. Pat. Nos.3,647,613; 3,862,284; 3,865,615; 4,020,223; 4,081,574; 4,142,032;4,296,151; 4,508,781; 4,536,266; 4,557,945; 4,764,405; and 4,869,859 aswell as published European Patent Application EP 0 21 4 635, and SouthAfrican Patents Nos. 85/9500 and 87/8240, at least some of whichdescribe techniques which can be adapted for the oxyfluorinationmentioned hereunder.

Preferably the activation is by surface fluorination, more preferablysurface oxyfluorination, and may be by exposing the surface to befluorinated to a fluorine-containing gas at a pressure of 5-150 kPa, andat a temperature typically of 20°-100° C. By oxyfluorination is meantthat the surface is provided with fluorine and oxygen substituents, egon --CH₂ and/or --CH₃ groups forming part of the surface. Thefluorine-containing gas may comprise fluorine itself (F₂), it maycomprise gaseous compounds containing fluorine such as CF₆ or SF₆, itmay comprise a fluorinated noble gas such as XeF₂, or it may comprise afluorohalogen such as CIF₃, BrF₅, IF₇, or the like. It should further benoted that both fluorination and oxyfluorination can in principle becarried out in inert liquid media in which a fluorinating compound suchas a fluorine-containing gas of the type mentioned above is dissolved,with or without oxygen (O₂ or O₃); The fluorine-containing gas may formpart of a mixture with other gases, such as oxides of sulphur, oxides ofnitrogen or oxides of carbon, halogens, interhalogens, nitrogen, oxygen,ozone or mixtures thereof, such as air. The proportion of thefluorine-containing gas in such gas mixture can vary within wide limits,the fluorine-containing gas forming 0,1-99,9% by volume of said mixture,typically forming 1-30% by volume thereof. Particularly preferred gasmixtures include those comprising 5-20% by volume of fluorinating gassuch as F₂ and 5-95% by volume oxygen (O₂ or O₃), so that the surfacefluorination is a surface oxyfluorination. The fluorination will usuallytake place in a reactor comprising a vacuum chamber with provision forfeeding thereto and withdrawal therefrom of gases, pressure control,temperature control and control of the composition of gas mixturestherein, and will normally be carried out batchwise. Accordingly, thefluorine-containing gas may form part of a mixture with other gases, thefluorine-containing gas forming 1-30% by volume of said mixture and thetemperature being 20°-100° C.; and in this case, as indicated above, thegas mixture preferably comprises 5-20% by volume of thefluorine-containing gas and 5-95% by volume of oxygen, so that thesurface fluorination is a surface oxyfluorination.

As indicated above, the surface fluorination may be such as to providethe surface activated component with a surface tension at 20° C. of atleast 40 mN/m, preferably at least 45 mN/m.

After the oxyfluorination of the surface, the surface may be subjectedto post-fluorination hydrolysis treatment, as far as possible tohydrolyse additional hydrolysable chemical functional groups on thesurface. In other words, after said oxyfluorination, the surface may besubjected to hydrolysis, to hydrolyse non-hydrolised chemical functionalgroups on the surface. The post-fluorination hydrolysis treatment may becarried out by bringing the fluorinated surface Into contact withatmospheric moisture for a sufficient period of time for a desireddegree of hydrolysis to occur, or by contacting the surface with anaqueous base for a sufficient period of time, or by contacting thesurface with an aqueous acid for a sufficient period of time, or bybringing the surface into contact with water for a sufficient period oftime, to obtain a desired degree of hydrolysis.

The resin used to impregnate the fibrous material (and/or to cause thefibrous material to adhere to the activated surface as describedhereunder) may be a curable settable thermosetting resin, eg a polyesteror an epoxy resin. Examples of polyester resins suitable in particularfor adhering the fibrous material to the activated surface are thoseavailable in South Africa as CRYSTIC 392 (isothalic neopentyl glycolunsaturated polyester resin), CRYSTIC 600 (bisphenolic unsaturatedpolyester resin) and CRYSTIC N7384PA (isothalic pre acceleratedunsaturated polyester resin) from NCS Resins, a division of SentrachemLimited. Generally, for the impregnation of the fibrous layer, anysuitable polyester resin is used. Examples of suitable epoxy resins foradhesion of the fibrous layer to the activated surface are thoseavailable in South Africa as PRO-STRUCT 7907 from Pro-struct, a divisionof KayMac Limited, DION 6694 and DION 9100 (bisphenol epoxy vinylesters) available from from NCS Resins, a division of SentrachemLimited, and DERAKANE 470 and DERAKANE 8084, epoxy vinyl ester resinsavailable in South Africa from Dow Chemical Company. An example of anepoxy resin which can be used for impregnating the fibrous material isPRO-STRUCT 988, also available from Prostruct.

Typically, the curing of the resin will comprise using a suitable curingagent or catalyst, eg a commercial curing system or package supplied by,and used in an amount as recommended by, the manufacturer of the resinused.

The resin-impregnated fibrous material may comprise inorganic fibres, egglass fibres or carbon (eg graphite) fibres. High tenacity syntheticplastics fibres, eg of a polyester, a polyolefin, or a polyamide such asKEVLAR (registered trade mark), may also be used. Mixtures of saidfibres may also be used. Both the inorganic and the synthetic fibres maybe fluorinated. Thus, the fibrous material may be subjected to surfacefluorination thereof prior to impregnation thereof with resin; and thefibrous material may have fibres which are selected from the groupconsisting of glass fibres, carbon fibres, polyester fibres, polyamidefibres, polyolefin fibres and mixtures thereof. The fibres may be in theform of chopped strand mat, unidirectional roving, woven roving orcontinuous roving.

According to an important feature of the invention, the reinforcingmaterial optionally comprises a plurality of resin-impregnated fibrouslayers, the layers adjacent and nearer the pipe or tank surface beingresin-rich and the layers further away from the pipe or tank surfacebeing resin-poor. Typically, the mass ratio of resin to fibres in thelayer nearest to the pipe or tank surface is greater than 70:30 and themass ratio of resin to fibres in the layer furthest away from the pipeor tank surface is less, being about 70:30 for chopped strand mat, about50:50 for unidirectional or woven roving, and about 30:70 for continuousroving. Typically the highest mass ratio of resin to fibres ismaintained for the first few millimetres thickness closest to theactivated surface, eg 1-2 mm. In other words, the process may comprisereinforcing the component with a plurality of resin-impregnated fibrouslayers, the mass ratio of resin:fibres in the layer closest to theactivated surface of the component being at least 70:30, preferably atleast 80:20 or more, such as 90:10 or more, and the mass ratio ofresin:fibres in the layer furthest from the activated surface of thecomponent surface being 70:30 - 30:70, said mass ratio decreasing in adirection away from the activated surface and normal thereto. By thismeans, a good wetting by the resin on the surface of the pipe or tank-isachieved which improves the adhesion of the resin to the pipe or tanksurface.

The surface of the pipe or the tank may be subjected to degreasing priorto fluorination thereof and/or after fluorination and prior to applyingthe layer of resin-impregnated material thereto to improve the adhesionof the wrapping material to the pipe surface or the tank surface.Accordingly, the surface may be subjected to degreasing prior to saidactivation thereof. Furthermore, the surface may, after said activationthereof and prior to the contacting, be subjected to decreasing. Ifdesired, the pipe or tank may be packaged after degreasing thereof untilthe pipe or tank is required to be subjected to fluorination and/or towrapping thereof by the resin impregnated material.

Suitable degreasing agents used to degrease the pipe surface or the tanksurface may be selected from acetone, ethanol, methyl ethyl ketone (MEK)and trichloro-ethylene (TCE). Water-soluble detergents can also be used.Naturally routine experimentation will be employed to determine whichdegreasing agents are compatible with the pipe surface or the tanksurface and with the resins employed in the process of the invention.

According to a further feature of the invention, to improve the adhesionof the wrapping material to the pipe surface or tank surface when theresin in the resin-impregnated fibrous wrapping material is a polyesterresin, one or more layers or coatings of an epoxy resin may be applied,eg by painting, to the activated surface of the pipe or tank prior toapplying the layers of polyester resin-impregnated fibres thereto. Theresin used to impregnate the fibrous material and the resin used tocause the fibrous material to adhere to the surface of the component maybe the same, or they may be different. Accordingly, causing the fibrousmaterial to adhere to the surface of the component may be by means of aresin which is different from the resin which impregnates the fibrousmaterial, each resin being selected from epoxy resins and polyesterresins. Instead, causing the fibrous material to adhere to the surfaceof the component may be by means of a resin which is the same as theresin which impregnates the fibrous material, each resin being selectedfrom epoxy resins and polyester resins.

Application of the resin-impregnated fibrous; layers to the fluorinatedsurface of the pipe or tank may be by hand lamination, tape wrapping orfilament winding.

Plastics pipes are widely used for the transport of fluids and thepressure in such pipes may vary from sub-atmospheric (vacuum) up to tensof atmospheres. Polyolefin pipes and tanks are reinforced by the processof the invention to increase their pressure rating and/or to increasetheir rigidity. For both purposes, the reinforcing process according tothe invention is similar. However, thicker layers of resin-impregnatedfibrous material are typically required to increase pressure rating.

For increasing the pressure rating of said polyolefin pipes, handlaminating or tape wrapping is conveniently started by coating theactivated surface with the resin (eg CRYSTIC 600, CRYSTIC 392 orPRO-STRUCT 7907) used to cause the impregnated fibrous material toadhere thereto. A layer of glass fibre chopped strand mat (i.e. achopped strand mat of glass fibres or filaments pressed together in amultidirectional manner) typically impregnated with a polyester resin orepoxy resin, is then typically laminated into place. These layers can bealternated, with layers of unidirectional roving or woven roving, orlaminating can be restricted to said chopped strand mat. The laminatingprocess is preferably finished with a glass or other synthetic fibretissue (eg a thin glass fibre mat) and the resin is cured according tothe resin manufacturer's specifications, to set it.

For increasing the rigidity of said polyolefin pipes or tanks, handlamination or tape wrapping is again conveniently started by coating theactivated surface with said CRYSTIC 600 or 392 or PRO-STRUCT 7907 resinsand laminated to the required thickness with chopped strand mat byitself or with chopped strand mat alternating with unidirectional rovingor woven roving. To finish the laminating process, said glass or othersynthetic fibre tissue is again used.

Filament winding is similar to the above hand laminating or tapewrapping process for increasing the pressure rating of said polyolefinpipes and increasing the rigidity of said polyolefin pipes and tanks,and only the thickness of laminating is changed if required. In filamentwinding, a glass fibre filament is dipped through a resin bath andwrapped on eg a pipe in one continuous strand unidirectionally along thepipe. The applicator arm then returns along the length of the pipeunidirectionally in the opposite direction. Thus, the filament isapplied in a bidirectional way.

While the three processes, i.e. hand lamination, tape wrapping andmachine filament winding, are substantially different, certain ratios offibre to resin, ratios of catalyst, temperature and many others remain acommon denominator. It will be appreciated that filament winding willnormally be more effective than hand lamination or tape wrapping.

The invention extends further to a component of plastics material whichis strengthened and reinforced by a resin-impregnated fibrous materialwhich adheres to a surface of the component, produced in accordance withthe process described above.

The invention will now be described, by way of non-limiting illustrativeexample, with reference to the following tests and experiments and withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plot of shear strength (MPa) against sample number forhigh density polyethylene pipe samples provided with a reinforcing ofepoxy resin-impregnated glass fibres or polyester resin-impregnatedglass fibres according to the process of the invention, with referenceto the required shear strength according to British Standard B.S. 6464to illustrate the strength profile of HDPE pipes;

FIG. 2 shows a plot of shear strength (MPa) against sample number forpolypropylene pipe samples provided with a reinforcing of epoxy-resinimpregnated glass fibres or polyester resin-impregnated glass fibresaccording to the process of the invention, with reference to therequired shear strength according to British Standard B.S. 6464 toillustrate the strength profile of PP pipes;

FIG. 3 shows a plot of shear strength (MPa) against sample number forhigh density polyethylene and polypropylene pipe samples provided with areinforcing of epoxy resin-impregnated fibres according to the processof the invention, with reference to the required shear strengthaccording to British Standard B.S. 6464 to illustrate the strengthprofile using an epoxy resin;

FIG. 4 shows a plot of shear strength (MPa) against sample number forhigh density polyethylene and polypropylene pipe samples having areinforcing of polyester resin-impregnated fibres according to theinvention, with reference to the required shear strength according toBritish Standard B.S. 6464 to illustrate the strength profile using apolyester resin;

FIG. 5 shows a plot of lap shear strength against pre-oxyfluorinationdegreasing time for TCE and MEK, the TCE results indicating apredominant platform failure after 10 hours;

FIG. 6 shows a plot of lap shear strength against oxyfluorination timefor PP;

FIG. 7 shows a plot of lap shear strength against oxyfluorination timefor HDPE;

FIG. 8 shows a plot of lap shear strength against oxyfluorinationpressure;

FIG. 9 shows a plot of lap shear strength for each of the resinmaterials when TCE is used as a degreasing agent and oxyfluorination isemployed;

FIG. 10 shows a plot of lap shear strength for each of the resinmaterials when TCE is used as a degreasing agent and fluorination isemployed;

FIG. 11 shows a plot of PAS units against hydrolysis time of HDPE and PP(IR peak=1848 cm⁻¹, baseline 2000-1532 cm⁻¹);

FIG. 12 shows a plot of relative PAS peak heights (REL) units againsthydrolysis time of HDPE and PP in air (IR peak=1844 cm⁻¹, base line2000-1532 cm⁻¹ ;

FIG. 13 shows lap shear strengths for various degreasing agents whenoxyfluorinated PP is employed and the resin is CRYSTIC 392;

FIG. 14 shows lap shear strengths for various degreasing agents whenoxyfluorinated PP is employed and the resin is CFRYSTIC 600;

FIG. 15 shows lap shear strengths for various degreasing agents whenoxyfluorinated PP is employed and the resin is DION 9100;

FIG. 16 shows lap shear strengths for various degreasing agents whenoxyfluorinated PP is employed and the resin is N7384PA; and

FIG. 17 shows a plot of lap shear strength against post-degreasingdrying time in hours when oxyfluorinattion is employed using MEK or TECas degreasing agent and the resin being CRYSTIC 392.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Push out tests were done on HDPE and PP pipe samples which were providedwith external reinforcing of epoxy resin-impregnated glass fibres by theprocess according to the invention. Similar tests were done on similarpipe samples provided with a similar reinforcing of polyesterresin-impregnated glass fibres by the process according to theinvention.

Five pipes were used, two HDPE pipes and three PP pipes. The HDPE pipeswere each 110 mm OD class 6 pipe having a wall thickness of 6 mm. TheHDPE was GM 5010 available from Megapipe, a division of Mega Plasticswhich in turn is a division of Sentrachem Limited. The PP pipes were 90mm OD class 4 pipe having a wall thickness of 5 mm. The PP was PPHI 2222available from Megapipe.

The HDPE pipes were reinforced in accordance with the process of theinvention by the following procedure. Half of the first pipe was knurled(roughened) on its outer surface while the other half was left smooth onits outer surface. The rough and smooth outer surfaces of pipe were thenfluorinated. The fluorination was carried out batchwise in an 11 m³ mildsteel reactor. A pipe sample was placed in the reactor and the reactorwas evacuated to an absolute pressure of 20 kPa. Then a F₂ /N₂ mixturecomprising 20% by volume F₂ was bled into the reactor to a totalpressure of 30 kPa. The fluorination was carried out at room temperaturefor 30 minutes, after which the reactor was evacuated and the sampleremoved. The fluorinated pipe was then wrapped by hand laminating with aglass fibre mat, either chopped strand or unidirectional rovingavailable from NCS Resins, a division of Sentrachem Limited, using anepoxy resin available as PRO-STRUCT 988 from Prostruct, a division ofKayMac Limited, to a thickness of 4 mm. Said PRO-STRUCT 988 was curedusing a commercial curing package supplied by, and used in. an amount asrecommended by, the manufacturer of PRO-STRUCT 988. The hand laminatinginvolved the application of the epoxy resin onto the pipe followed by alayer of the glass fibre mat. The process was continued, alternatingbetween the glass and the resin until said thickness was achieved, afterwhich a final layer of a thin layer of tissue (thin glass fibre mat),available from NCS Resins, was applied. It is important in this processto eliminate all air bubbles from between the layers of glass and resin,by rolling them out with special applicator rollers commonly used in theindustry. For the first 1-2 mm of the wrapping, the resin to glass massratio was 50:50 and was then changed to 30:70 until the thickness of 4mm was obtained.

The second HDPE pipe was roughened on half of its outer surface, and therough and smooth outer surfaces were fluorinated, in the same way asdescribed for the first HDPE pipe. After fluorination, the pipe waswound by hand laminating with said glass fibre mat using a polyesterresin available as CRYSTIC 600 from NCS Resins to a thickness of 5 mm.This treatment was less labour intensive than that for the first HDPEpipe. The hand laminating process was similar to that used for the firstHDPE pipe, using a curing package supplied by, and used in an amountrecommended by, the supplier of CRYSTIC 600.

The PP pipes were treated and wrapped in a similar fashion, except thatone was wrapped using said epoxy resin and two were wrapped using saidpolyester resin, one at low temperature (±20°0 C.) and one at hightemperature (±26° C.).

The pipes were cut into 60 mm lengths to form samples numbered asfollows: ##STR1##

A 15 mm length of the HDPE or PP was machined out of each end of each 60mm length for the purposes of push out tests conducted in accordancewith B.S. 6464. The push out tests involved the remaining length of theHDPE or PP pipe of the test pieces being pushed out of the overwrappingand measuring the force required to do so. The shear strength or"push-out" strength was then calculated as follows: ##EQU1## whereF=maximum force required to shear the pipe from the overwrapping N!

d=pipe outerdiameter (mm)

h=remaining encapsulated plastics liner length (mm)

The push out test results are summarised in Table 1 below. Thesupporting strength profiles viz. the strength profile of the HDPE pipesamples, the strength profile of the PP pipe samples, the strengthprofile of the pipe samples using epoxy resin and the strength profileof the pipe samples using polyester resin are shown in the accompanyingFIGS. 1 to 4 respectively. Each of FIGS. 1-4 shows for comparison therequired shear strength according ito the British Standard B.S. 6464.

Table 1 also shows the average shear forces, taking all the testresults, as well as the average when disregarding the highest and lowestvalues. The standard deviation and variance is also shown, and thenfinally, whether or not the shear strength of the pipe samples matchesor exceeds that specified by B.S. 6464.

From Table 1, it can be seen that the smooth PP pipe samples wrappedusing the polyester resin comply with B.S. 6464. The other pipe samples,though not complying to B.S. 6464, fared well.

Detailed results, with the parameters used in the calculation are givein Tables 2-7 below.

                                      TABLE 1                                     __________________________________________________________________________    SUMMARY OF RESULTS OF THE PUSH OUT TESTS                                      SAMPLE SHEAR STRENGTH (MPa)                                                   NO.    1  2  3  4  5  6  7  8  9  10                                          __________________________________________________________________________    1      5.5                                                                              5.1                                                                              4.4                                                                              4.4                                                                              4.7                                                                              6  7.9                                                                              5.02                                                                             8.9                                                                              6.71                                        2      6.75                                                                             5.41                                                                             5.3                                                                              4.5                                                                              4.6                                                                              5.5                                                                              6.9                                                                              6.3                                                                              9.1                                                                              5.83                                        3      6.78                                                                             5.21                                                                             4.75                                                                             4  5.5                                                                              6.3                                                                              7.8                                                                              5.98                                                                             9.2                                                                              6.36                                        4      5.72                                                                             6.42                                                                             4.8                                                                              4  6  6.1                                                                              6.4                                                                              6.8                                                                              8  6.37                                        5      5.57                                                                             5.69                                                                             4.8                                                                              4.6                                                                              5.6                                                                              6.9                                                                              8.2                                                                              6.5                                                                              8.6                                                                              7.11                                        Average                                                                              6.06                                                                             5.57                                                                             4.81                                                                             4.3                                                                              5.28                                                                             6.16                                                                             7.44                                                                             6.12                                                                             8.76                                                                             6.48                                        Average 1                                                                            6.01                                                                             5.44                                                                             4.78                                                                             4.3                                                                              5.21                                                                             6.13                                                                             7.53                                                                             6.26                                                                             8.87                                                                             6.48                                        Std devn                                                                             0.58                                                                             0.47                                                                             0.29                                                                             0.25                                                                             0.54                                                                             0.45                                                                             0.68                                                                             0.61                                                                             0.43                                                                             0.42                                        Variance                                                                             0.33                                                                             0.22                                                                             0.08                                                                             0.06                                                                             0.29                                                                             0.21                                                                             0.46                                                                             0.37                                                                             0.19                                                                             0.18                                        Acceptable                                                                           NO NO NO NO NO NO YES                                                                              NO YES                                                                              NO                                          __________________________________________________________________________     Legend                                                                        1 PE In Epoxy resin  smooth                                                   2 PE In Epoxy resin  rough                                                    3 PP In Epoxy resin  smooth                                                   4 PP In Epoxy resin  rough                                                    5 PE In Polyester resin  smooth                                               6 PE In Polyester resin  rough                                                7 PP In Polyester resin  smooth 1 (low temperature wrapping ±              20° C.)                                                                8 PP In Polyester resin  rough 1 (low temperature wrapping ± 20.degree     C.)                                                                           9 PP In Polyester resin  smooth 2 (high temperature wrapping ±             26° C.)                                                                10 PP In Polyester resin  rough 2 (high temperature wrapping ±             26° C.)                                                                Average 1 Highest and lowest not Included                                

                  TABLE 2a                                                        ______________________________________                                        Epoxy Resin/HDPE (smooth)                                                             HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       31       110        59.7    5.5                                       2       30       110        70.0    6.75                                      3       30       110        70.3    6.78                                      4       31       110        59.3    5.72                                      5       30       110        57.8    5.57                                      ______________________________________                                    

                  TABLE 2b                                                        ______________________________________                                        Epoxy Resin/HDPE (rough)                                                              HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       30       110        52.8    5.10                                      2       31       110        57.9    5.41                                      3       31       110        55.8    5.21                                      4       30       110        66.5    6.42                                      5       30       110        58.0    5.69                                      ______________________________________                                    

                  TABLE 3a                                                        ______________________________________                                        Polyester/HDPE (smooth)                                                               HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       29       110        47.2    4.7                                       2       29       110        46.1    4.6                                       3       29       111        56.0    5.5                                       4       29       111        61.4    6.0                                       5       29       110        56.1    5.6                                       ______________________________________                                    

                  TABLE 3b                                                        ______________________________________                                        Polyester/HDPE (rough)                                                                HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       29       110        60.2    6.0                                       2       29       110        54.7    5.5                                       3       29       110        63.7    6.3                                       4       30       110        63.1    6.1                                       5       29       110        69.0    6.9                                       ______________________________________                                    

                  TABLE 4a                                                        ______________________________________                                        CRYSTIC 600 (dark)/PP (rough)                                                         HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       31       89         58.2    6.71                                      2       29       90         48.28   5.83                                      3       30       90         54.0    6.36                                      4       30       89         55.2    6.37                                      5       30       89         61.6    7.11                                      ______________________________________                                    

                  TABLE 4b                                                        ______________________________________                                        CRYSTIC 600 (dark)/PP (smooth)                                                        HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       30       90         75.7    8.9                                       2       30       90         77.4    9.1                                       3       29       89         77.9    9.2                                       4       31       89         69.7    8.0                                       5       30       90         73.1    8.6                                       ______________________________________                                    

                  TABLE 5a                                                        ______________________________________                                        CRYSTIC 600 (lighter)/PP (rough)                                                      HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       31       90         44.0    5.02                                      2       30       89         53.2    6.3                                       3       30       90         50.71   5.98                                      4       29       90         56.0    6.8                                       5       30       90         55.5    6.5                                       ______________________________________                                    

                  TABLE 5b                                                        ______________________________________                                        CRYSTIC 600 (lighter)/PP (smooth)                                                     HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       30       90         67.3    7.9                                       2       30       90         58.6    6.9                                       3       29       90         64.1    7.8                                       4       31       89         55.8    6.4                                       5       30       90         69.3    8.2                                       ______________________________________                                    

                  TABLE 6a                                                        ______________________________________                                        Epoxy/PP (smooth)                                                                     HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       31       90         38.37   4.4                                       2       30       90         45.48   5.3                                       3       30       89         39.82   4.75                                      4       31       90         41.98   4.8                                       5       30       90         40.37   4.8                                       ______________________________________                                    

                  TABLE 6b                                                        ______________________________________                                        Epoxy/PP (rough)                                                                      HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       30       89         36.72   4.4                                       2       30       89         37.98   4.5                                       3       30       89         33.4    4.0                                       4       30       90         34.05   4.0                                       5       29       90         37.84   4.6                                       ______________________________________                                    

Table 7 below, there are presented detailed results similar to Tables2-6 above using smooth HDPE and PP pipe samples overwrapped by machinewrapping using said epoxy resin PRO-STRUCT 988. A glass filament wasdipped in a bath of the epoxy/curing system and wrapped on the pipe inone continuous strand unederectionally along the pipe. The applicatorarm then moved along the length of the pipe unidirectionally in theopposite direction. Thus, the filament was applied in a bidirectionalway. The general thickness of the laminate was 5 mm. After curingaccording to the manufacturer's specifications, the test samples weresubjected to push out tests as described above.

                  TABLE 7a                                                        ______________________________________                                        Epoxy/HDPE                                                                    Machine Wrapping                                                                      HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       31.0     112.0      44.69   4.31                                      2       29.4     111.0      18.75   1.83                                      3       30.5     112.0      49.52   4.81                                      ______________________________________                                    

                  TABLE 7b                                                        ______________________________________                                        Epoxy/PP                                                                      Machine Wrapping                                                                      HIGHEST                                                                       VALUE    PIPE       MAXIMUM                                                   OF PIPE  OUTER      SHEAR   SHEAR                                     SAMPLE  LENGTH   DIAMETER   FORCE   STRENGTH                                  NO.      mm!      mm!        N!      MPa!                                     ______________________________________                                        1       30.0     110.0      40.2    3.68                                      2       29.5     110.4      58.7    5.72                                      3       29.5     111.0      87.1    8.12                                      ______________________________________                                    

The various experiments described below serve to demonstrate the effectof various process variables on the process of the invention. Theeffects of these variables are expressed in terms of final lap shearadhesive strength achieved by varying the relevant process variablewhile keeping the remaining variables constant. A different quantifyingtechnique was used to evaluate the effect of changes in specificvariables when hydrolysis times were investigated, in conjunction withthe shear strength test technique as hereinbefore described.

Lap shear adhesive strengths were derived from adhesive strengthsobtained by applying polyester by itself (ie without glass fibrereinforcing) to masked areas on plastics sheet surfaces 26 mm wide andeither 10 mm or 15 mm long (overlap length) and measuring the lap shearstrengths thereof. The plastics sheets used to manufacture the lap shearjoints were 60 mm long, 26 mm wide and 2 mm thick. The reverse sides ofthe sheets were glued to 26 mm wide and 6.25 mm thick steel backingplates by means of an epoxy resin over the full length and width of eachsheet. The purpose of the steel backing plate was to eliminate theoccurrence of any turning moment in the overlap joint of the plasticssheet under stress, and also to reduce or eliminate any peelingcharacteristics in the lap shear test. A further purpose of the steelplate was to serve as a mechanical attachment for the application of ashear force in the mechanical test apparatus (insron 4465 tensometerfitted with a 5 kN load cell). Each test co-ordinate was derived from anaverage of five (quintuplet) lap shear strength tests.

All resins used were obtained from NCS Resins, a division of SentrachemLimited and are set out below:

Crystic N7384PA--isothalic pre accelerated unsaturated polyester resin.

Dion 9100 --Bisphenol epoxy vinyl ester.

Crystic 392 --isothalic neopentyl glycol unsaturated polyester resin.

Crystic 600--Bisphenolic unsaturated polyester resin.

The plastics sheet material samples used were:

1) 2 mm thick black pigmented GMS010 based HDPE-PE300 obtained fromMaizey Plastics (Proprietary) Limited, Pretoria, Republic of SouthAfrica

2) 22 mm thick natural colour PP (PP 1022) - also obtained from MaizeyPlastics (Proprietary) Limited, Pretoria, Republic of South Africa.

Effect of Degreasing PP Surfaces Prior to Oxyfluorination

Pipe surfaces were cleaned of oil and dust contaminants to facilitateeffective activation (by means of oxyfluorination) of the pipe surfaces.Degreasing can be an important step owing to possible contamination ofpipe surfaces during pipe production (by extrusion equipment) as well asduring the handling of pipes thereafter during transit and storage.Degreasing can also act to remove surface blooms arising from processingadditives and performance stabilizers such as antioxidants which canbleed on to pipe surfaces. It should also be noted that, forindustrial-scale applications, chemical degreasing can be supplementedor replaced by mechanical degreasing, eg by means of rotating brushessimilar to car-wash brushes.

The following experimental conditions were employed:

Evaluation method: Lap shear tests.

Degreasing agent: MEK (methyl ethyle ketone) and TCE (trichloroethylene)

Pipe Material: PP (PPH1022) from Megapipe

Degreasing method: Immersion in degreasing agent at room temperature for5 minutes was followed by wiping of the surface with degreasingagent-darnpened tissue paper, followed by air drying at ambientconditions.

Drying time before oxyfluorination: Variable between 5 minutes and 24hours.

Surface Activation: 10 kPa air+40 kPa F₂ /N₂ mixture comprising 15% F₂by volume for 0.5 hours at 50° C.

PP Surface area to gas volume relation-ship: 300 cm² /2600 cm³.

Hydrolysis technique for oxyfluorinated surface: Immersion immediatelyafter oxyfluorination in demineralised water at room temperature for 18hours.

Drying of surface after hydrolysis: 24 hours natural air drying atambient conditions (exposure to ambient air).

Lap shear overlap dimensions: length: 10 mm, width: 26 mm.

Resin: Crystic 392.

The lap shear strengths of the bonds formed as a function ofpre-oxyfluorination degreasing time are shown in Table 8 below and inFIG. 5.

                  TABLE 8                                                         ______________________________________                                                   TCE DEGREASING: MEK DEGREASING:                                               LAPSHEAR        LAPSHEAR                                           TIME (hours)                                                                             STRENGTH (MPa)  STRENGTH (MPa)                                     ______________________________________                                        0.083      8.3             6.4                                                0.5        8.4             7.8                                                1          10.2            9.5                                                2          9.7             8.8                                                4          10.4            8.6                                                7          11.1            8.7                                                24         5.8             8.1                                                ______________________________________                                    

When TCE was used for degreasing, the tests demonstrated a 60-70%failure rate at the epoxy/PP interface rather than at the polyester/PPinterface. From this result and with reference to the results when MEKwas used it appears possible that:

a) Excessively thorough degreasing (eg vapour degreasing) with TCE canbe disadvantageous when epoxy resin is used.

b) The values shown above when TCE was used represent minimum shearstrength values between Crystic 392 polyester and the oxyfluorinated PPsurface. The marked decrease in resin strength arising from long dryingtimes (24 hrs) may not necessarily be representative of the polyester/PPresin strength.

Pre-oxyfluorination degreasing with MEK resulted in relatively pooraverage (8.5 MPa) lap shear strength when compared with using TCE overthe complete drying-time range. Substantially similar tests had earlierrepeatedly given lap shear strengths in excess of 13 MPa, whenoxyfluorinated PP was lightly degreased with TCE at least 3 weeks beforeoxyfluorinadon. It is believed that the use of other degreasing agents(or even soaps) prior to oxyfluorination, can influence the process invarious ways, the influence being dependent on the degreasing agent usedas well as on the time interval between degreasing andfluorination/oxyfluorination, and on the regime to which the PP surfaceis exposed. It should further be noted that degreasing can also inprinciple be carried out using water-soluble detergents, prior tosurface fluorination or oxyfluorination. In small-scale tests Handy Andyhousehold detergent, available in South Africa from Lever Industrial(Proprietary) Limited has been used successfully.

Effect of Varying Oxyfluorination Conditions on Lap Shear Strength of aPolyester-Oxyfluorinated Polyolefin Bond.

Plastics pipe outer surfaces were degreased and cleaned of anycontaminants, eg dust etc.

Effect of Oxyfluorination Time and Temperature

The following experimental conditions were employed:

Evalution method: Lap shear tests

Material: PP (PPH 1022) and HDPE (black GM5010 based PE300)

Degreasing agent: TCE

Degreasing method: Surface was wiped with TCE-dampened paper tissue.

Drying time before oxyfluorination: Approximately 3 weeks.

Oxyfluorination:

a) 40 kPa F₂ /O₂ mixture comprising 20% by volume F₂ at 50° C.

b) 40 kPa F₂ /O₂ mixture comprising 20% by volume F₂ at 20° C.

Oxyfluorination time: Variable between 10 seconds and 1 hour.

Polyolefin surface area to gas volume relationship: 300 cm² /2600 cm³.

Hydrolysis of oxyfluorinated surface: Immersion immediately afteroxyfluorination in demineralised water at room temperature for 18 hours.

Drying of surface after hydrolysis: 24 hours natural air drying atambient conditions.

Lap shear overlap dimensions: length: 10 mm, width: 26 mm.

Resin: Crystic 392.

Tabulated lap shear strength results for the pipe samples at the twotemperatures are shown in Table 9 below.

                  TABLE 9                                                         ______________________________________                                        Lap Shear Strengths (MPa)                                                     Oxy-     PP oxy-  PP oxy-  HDPE     HDPE                                      fluorination                                                                           fluorinated                                                                            fluorinated                                                                            oxyfluorinated                                                                         oxyfluorinated                            time (minutes)                                                                         at 50° C.                                                                       at 20° C.                                                                       at 50° C.                                                                       at 20° C.                          ______________________________________                                        0.16     9.6      12.2     5.2      5.4                                       0.5      11.2     14.8     6.7      7.9                                       1        13.5     12.2     9.1      10.1                                      4        11.05    13.8     10.6     11.5                                      10       12.4     11.6     11.1     11.5                                      20       10.7     14.5     10.1     12.6                                      30       13.1     13.3     13.3     10.5                                      60       10.6     13.8     9.9      11.5                                      ______________________________________                                    

The data in Table 9 are illustrated in FIGS. 6 and 7 for PP and HDPErespectively.

The minimum time (independent of the two temperatures investigated)required for sufficient or adequate surface activation of the PP surfaceat the experimental pressures was less than 5 seconds. Factors thatcould influence this minimum time possibly include the presence ofadditives in the PP.

At both temperatures, it is apparent that in the case of black pigmentedHDPE (PE300), a minimum time of between 1 and 10 minutes was requiredsufficiently or adequately to activate the surface.

In the case of both PP and HDPE, these minimum times can be influencedby the F₂ :O₂ ratio and total pressure used.

Effect of Oxyfluorination Pressure.

The following experimental conditions were employed:

Evaluation method: Lap shear tests.

Material: PP (PPH1022) and HDPE (black GM5010 based PE300).

Degreasing agent: TCE.

Degreasing method: Surface was wiped with TCE-dampened paper tissue.

Drying time before oxyfluorination: Approximately 3 weeks.

Oxyfluorination: A F₂ /O₂ mixture comprising 20% by volume F₂ was usedat 50° C. and 20° C. for 0.5 hrs.

Oxyfluorination pressure: Variable between 0.5 kPa and 80 kPa.

Polyolefin Surface area to gas volume relationship: 300 cm² /2600 cm³

Hydrolysis of oxyfluorinated surface: Immersion immediately afteroxyfluorination in demineralised water at room temperature for 3 hours.

Drying of surface after hydrolysis: 24 hours natural air drying atambient conditions.

Lap shear overlap dimensions: length: 10 mm, width: 26 mm.

Resin: Crystic 392.

Tabulated lap shear strength results for the PP and HDPE at the variouspressures are shown in Table 10 below.

                  TABLE 10                                                        ______________________________________                                        OXYFLUORI-                                                                    NATION   LAP SHEAR STRENGTH                                                                            LAP SHEAR STRENGTH                                   PRESSURE ON PP (MPa)     ON HDPE (MPa)                                        (kPa)    50° C.                                                                           20° C.                                                                           50° C.                                                                         20° C.                            ______________________________________                                        0.5      13.2      10.7      6.4     4.0                                      2        11.9      12.4      8.7     4.1                                      10       13.9      10.6      10.3    10.9                                     20       14.7      13.8      11.2    9.9                                      50       14.2      13.2      9.0     7.4                                      80       14.3      12.9      11.4    8.9                                      ______________________________________                                    

The shear strength for 50 kPa at 20° C. was possibly unreliable.

The 50° C. results are illustrated in FIG. 8.

PP showed appreciably higher bond strengths than HDPE. It is believedthat this is due to the higher reactivity of PP when oxyfluorinated dueto its higher number of end groups as well as the fact that the PP isfree of black pigment. HDPE appears to require at least 2 kPa at 50° C.and 10 kPa at 20° C. for sufficient or adequate surface activationthereof. It is possible that PP requires less than 0.5 kPa of the F₂ /O₂mixture at the experimental conditions for sufficient or adequatesurface activation thereof. It thus appears that increases in fluorine(F₂) partial pressures are substantially more effective than increasesin temperature, to obtain quick activation of the polyolefin surface.

Fluorination Versus Oxyfluorination as Surface Activation Technique forAdhesion

Fluorination involves treating plastics pipe surfaces with purefluorine, or a fluorine and inert gas (eg nitrogen, helium, argon etc)mixture, or a fluorinecontaining gas such as XeF₂, CIF₃, BrF₅, IF₇, CF₄,SF₆ or the like. Oxyfluorination in turn involves surface activationwith a gas mixture of which at least two of the components are afluorine source such as those mentioned above for fluorination, andoxygen (or an oxygen containing gas) respectively, ie at least onefluorine component and at least one oxygen component. In principle bothfluorination and oxyfluorination can take place with the reagent gasesdissolved in a suitable inert liquid solvent such as a FREON which iscontacted with the polyolefin surface.

The following experimental conditions were employed:

Evaluation method: Lap shear tests.

Material: HDPE (black GM5010 based PE300).

Degreasing agent: TCE.

Degreasing method: Pipe surfaces were wiped with TCE-dampened papertissue.

Drying time before oxyfluorination and fluorination: Two days.

Oxyfluorination conditions: 50° C. for 0.5 hrs.

Oxyfluorination pressure: 10 kPa air+20 kPa F₂ /O₂ mixture comprising20% by volume F₂.

Fluorination conditions: 50° C. for approximately 3 hrs.

Fluorination pressure: A F₂ /N₂ mixture comprising 20% by volume F₂ wasused at a pressure sufficient to give the surface a fluorine massloading of 60μg/cm² after fluorination.

Hydrolysis of activated surface: Hydrolysis by exposure to moisture inambient air for longer than 2 months.

Lap shear overlap dimensions length: 15 mm, width: 26 mm.

Resins: Crystic 392, Crystic 600, N7384PA, Dion 9100.

The results demonstrating differences in resin adhesive strength for thetwo activation techniques (fluorination and oxyfluorination) are shownin Table 11 below and are illustrated in FIG. 9 (oxyfluorination) andFIG. 10 (fluorination).

                  TABLE 11                                                        ______________________________________                                                  Oxyfluorinated substrate                                                                       Fluorinated substrate                                        Lap shear strength                                                                             Lap shear strength                                 Resin     (MPa)            (MPa)                                              ______________________________________                                        Crystic 392                                                                              9.9             6.1                                                Crystic 600                                                                             10.4             3.5                                                Dion 9100 11.6             10.9                                               N7384PA   10.4             4.6                                                ______________________________________                                    

Oxyfluorination resulted in higher lap shear resin adhesive strengthswith a broader range of resins when compared to fluorination. Withcertain resins, (eg Dion 9100), a fluorinated surface was shown to becapable of providing resin adhesive strengths comparable with those ofan oxyfluorinated surface.

Effect of Hydrolysis Conditions on Lap Shear Strength

Immediately after oxyfluorination an activated polyolefin surfaceundergoes a hydrolysis reaction when brought into contact withatmospheric air. During this hydrolysis, the surface is chemicallyunstable and generally unsuitable for the application of resin.Accelerated hydrolysis is thus desirable.

Determination of the Optimum Hydrolysis Medium

The following experimental conditions were employed:

Evaluation method: Lap shear tests.

Material: PP (PPH1022) and HDPE (black GM5010 based PE300).

Degreasing agent: TCE.

Degreasing method: Surface was wiped with TCE-dampened paper tissue.

Drying time before oxyfluorination: Approximately 3 weeks.

Oxyfluorination conditions: 40kPa F₂ /O₂ mixture comprising 20% byvolume F₂ at 50° C. for 0.5 hrs.

Polyolefin surface area to gas volume relationship: 300 cm² /2600 cm³

Hydrolysis of activated surface: Immersion immediately afteroxyfluorination in hydrolysis medium.

Hydrolysis mediums investigated at 20° C.:

0.5M aqueous NaOH solution for 120 minutes.

0.5M aqueous HCl solution for 120 minutes.

Demineralised water for 120 minutes.

Atmospheric water vapour for 69 hrs.

Drying of surface after hydrolysis: 24 hours natural air drying atambient conditions.

Lap shear overlap dimensions: length: 10 mm, width: 26 mm.

Resin: Crystic 392.

Tabulated lap shear strength results for the PP and DHPE and hydrolysismedia are shown in Table 12 below.

                  TABLE 12                                                        ______________________________________                                        Hydrolysis                                                                           Lap shear strength on PP                                                                       Lap shear strength on HDPE                            medium (MPa)            (MPa)                                                 ______________________________________                                        Air    12.8             8.0                                                   H.sub.2 O                                                                            12.5             8.2                                                   HCl    11.6             9.2                                                   NaOH   11.8             7.9                                                   ______________________________________                                    

In the case of PP, air and water hydrolysis gave slightly higher bondstrengths with Crystic 392, while in the case of HDPE, water and HClgave marginally higher values. From a practical point of view, itappears that water would be the preferred choice of hydrolysis medium.Practical issues include cost, ease of handling and time required forsubstantially full hydrolysis of the surface. Water effectedsubstantially full hydrolysis in less than 3 hours compared to airhydrolysis which required up to 120 hours.

Determination of Minimum Hydrolysis Times for Different HydrolysingMedia

A freshly activated surface typically contains acyl fluoride chemicalfunctional groups that undergo hydrolysis. During hydrolysis theactivated surface is regarded as being unstable. PP and HDPE surfaceswere oxyfluorinated with 100 kPa F₂ /O₂ mixture comprising 20% by volumeF₂ at 50° C. for 16 hours. A decrease in infrared peak intensity of theacyl fluoride functional groups on the surface was monitored as afunction of exposure time in the hydrolysation medium. For this purposea Fourier transform infrared-photoacoustic spectrum (FTIR-PAS) techniquewas used as a quantifying technique. The hydrolysing media used were0.05M solutions of HCI and NaOH, as well as pure demineralised water andambient air.

The results for HCI and water hydrolysis on PP and HDPE surfaces areshown in FIG. 11. The results for air hydrolysis are shown in FIG. 12.The aqueous hydrolysis medium results are tabulated in Table 13, andnormalised FTIR-PAS peak heights (1844 wrt±3000 cm⁻¹), corresponding toair hydrolysis, are shown in Table 14. No data were obtained for NaOHsince immersion in this hydrolysing medium resulted in an immediatedrastic reduction in IR band intensities.

                  TABLE 13                                                        ______________________________________                                        FTIR-PAS peak heights at 1844 cm.sup.-1                                            Oxyfluorinated                                                                           Oxyfluorinated                                                                           Oxyfluorinated                                                                         Oxyfluorinated                            Time PP in      PP in      HDPE in  HDPE in                                   (min)                                                                              HCl solution                                                                             water      HCl solution                                                                           water                                     ______________________________________                                          0  5.5        5.5        3.9      3.9                                         5  3.9        4.1        --       --                                          6  --         --         2.1      1.4                                        15  --         --         2.1      1.3                                        25  2.5        2.4        --       --                                         30  --         --         1.7      0.9                                        60  --         --         0.8      0.7                                        72  2.1        2.2        --       --                                         120 --         --         0.8      0.7                                        200 --         1.9        --       --                                        1440 0.8        1.1        --       --                                        1680 --                     0.32     0.02                                     ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        Normalised FTIR-PAS peak heights at 1844 cm.sup.-1                            Time                                                                          (hrs)     Oxyfluorinated HDPE                                                                         Oxyfluorinated PP                                     ______________________________________                                         0        0.55          0.5                                                    4        0.51          0.47                                                   24       0.39          0.29                                                   31       0.24          0.27                                                   72       0.14          0.20                                                   79       0.13          --                                                    168       0.08          --                                                    ______________________________________                                    

FTIR-PAS has a substrate penetration depth of approximately 20 microns(μm) in the frequency domain of the acyl fluoride absorption band. It isbelieved that adhesion primarily involves the outer 1 nm depth ofmaterial under the oxyfluorinated surface, and that the times requiredto achieve stabilisation in the above results represent the timesrequired to achieve maximum hydrolysation in the respective media. Foroxyfluorinated PP and HDPE, water and HCl each hydrolysis took less than3 hrs, and in the case of air, hydrolysis took less than 120 hrs.

Determination of the Optimum Drying Time with Water as Hydrolysis Medium

After hydrolysis in either an aqueous HCl solution or in water, thesurface of a component should be dried before the application of theresin can take place. After HCl-medium hydrolysis the surface should berinsed with water to remove any residual acid thereon, before drying.

The following experimental conditions were employed:

Evaluation method: Lap shear tests.

Material: PP (PPH1022).

Degreasing agent: TCE.

Degreasing method: Surface was wiped with TCE-dampened paper tissue.

Drying time before oxyfluorination: Approximately 3 weeks.

Oxyfluorination: 40 kPa F₂ /O₂ mixture comprising 20% by volume F₂ at50° C. for 0.5 hrs.

Polyolefin surface area to gas volume relationship: 300 cm² /2600 cm³

Hydrolysis of activated surface: Immersion immediately afteroxyfluorination in hydrolysis medium at room temperature for 18 hrs.

Hydrolysis medium: Demineralised water

Drying time of surface after hydrolysis: Variable between 5 minutes and24 hrs.

Lap shear overlap dimensions: length: 10 mm, width: 26 mm.

Resin: Crystic 392.

It Is believed that the epoxy resin used to join the shear test sheetsto the backing plates is adversely affected or influenced by a wetsurface. The backing plates were therefore first joined to the sheets inusual fashion before tests were conducted. Different drying times werethen simulated by wetting the surface with a water-dampened tissue andthen allowing various times to elapse before the polyester resin wasapplied to the test surfaces.

Table 15 below demonstrates the effect of varying post-hydrolysis dryingtimes of the surface before application of the polyester resin.

                  TABLE 15                                                        ______________________________________                                        Drying time  Lap shear strength                                               (hours)      (MPa)                                                            ______________________________________                                          0.25       10.1                                                             1             9.4                                                             3             9.0                                                             6            14.5                                                             ______________________________________                                    

Given the inherent scatter in results characteristic of the lap sheartest method, the values obtained in the time interval between andincluding 0.25 to 3 hours do not represent a significant trend. Theimprovement at 6 hours, however, indicates improved adhesion. Dryingtimes, at ambient conditions, in excess of 3 hours, are thus desirableafter hydrolysis, in order to achieve optimum adhesion. However, dryingtimes less than 3 hours showed adhesion which was not unacceptable.Because ambient conditions change from day to day, as well as withseasons and location, the above results are expected to vary, withinlimits.

Comparison Between Commercially Available Fleece-Backed PP Sheeting andOxyfluorinated PP Sheeting in Terms of Lap Shear Strength Using aPolyester Reson

So-called fleece-backed PP sheeting is typically used to manufacturelarge container reservoirs in industry.

Due to low wettabilities, low surface energies induced by low polaritiesand low interactions across interfaces, polyolefins generally do nothave good adhesion properties. To facilitate use of polypropylene inadhesion applications, a polyester fleecing is attached to thepolypropylene. The polyester fleecing improves the wettability of thesurface and provides mechanical interlocking sites for the resin usedfor the adhesion. The main application of fleecing is in the manufactureof large storage tanks (fleecing on the outside), eg to store aggressiveor corrosive chemicals. The tanks are then reinforced with polyesterresin-impregnated glass fibre. This construction technique provides theuser with a strong storage tank that is resistant to various chemicals.

MATERIALS USED

a) Commercially available polypropylene:- Trovidur PP 7032 (Grey)obtained in South Africa from lntematio (Proprietary) Limited,Krugersdorp.

b) Commercially available polypropylene (Amparglas):- PPH 1022 (Natural)obtained from Ampaglas South Africa (Proprietary) Limited.

c) Commercially available fleece-backed polypropylene:- Trovidur PPN7032 obtained from intematio (Proprietary) Limited.

The following experimental conditions were employed:

The various polypropylene surfaces were degreased with TCE and allowedto dry.

Fluorination Conditions of Non-fleeced Materials:

a) Gas Mixture: 10 kPa Air, 10 kPa N₂, 30 kPa F₂ /N₂ mixture comprising15.8% by volume F₂

b) Fluorination Temperature: 50° C.

c) Fluorination Time: 30 minutes

Hydrolysis Conditions:- 1 week exposure to moisture in ambient air

Resins Used:- Crystic 600 and Crystic 392

Evaluation Method:- Lap Shear Tests

Silicone sealant was used as a masking agent on the fleece-backedsamples since the polyester fleecing absorbed the polyester resinsthereby making testing very difficult. The silicone sealant preventedabsorption of the polyester resin and did not adhere to the resinstested. A laminate was then made using polyester resin and three layersof surface tissue made from non-woven glass fibre veil material, to forman unmasked shear area of 312 mm² (26 mm width×12 mm length). Thevarious laminates were then tested.

The lap shear results for the various grades of polypropylene are setout in Table 16 below.

                                      TABLE 16                                    __________________________________________________________________________    Lap shear results obtained for polypropylene                                  Lap Shear Strength (MPa)                                                      Trovidur PP/V 7032                                                                            Trovidur PP 7032                                                                         PPH 1022                                           Sample     Crystic                                                                            Crystic                                                                            Crystic                                                                             Crystic                                                                            Crystic                                       Number                                                                             Crystic 600                                                                         392  600  392   600  392                                           __________________________________________________________________________    1    8.244 4.144                                                                              12.12                                                                              10.61 9.113                                                                              14.20                                                         Substrate                                                     2    7.766 3.885                                                                              11.45                                                                              9.153 12.00                                                                              11.89                                                         Substrate                                                     3    9.769 3.958                                                                              8.413                                                                              7.112 13.03                                                                              11.32                                         4    6.913 4.282                                                                              Platform                                                                           Poor  10.25                                                                              12.56                                                         Failure                                                                            Glue-line                                                5    Platform                                                                            Platform                                                                           Platform                                                                           Poor  Platform                                                                           Poor                                               Failure                                                                             Failure                                                                            Failure                                                                            Glue-line                                                                           Failure                                                                            Glue-                                                                         line                                          Average                                                                            8.173 4.067                                                                              10.66                                                                              8.959 11.10                                                                              12.49                                         __________________________________________________________________________

Based on the above laps shear strength results it is evident that byusing fluorine surface-treated PPH 1022 material optimum cost (as thePPH 1022 material is the least expensive) and performance benefits canbe obtained.

Further push-out tests of the general type described above, withreference to Tables 1-7 and FIGS. 1-4 were carried out, and aredescribed in Examples 1-6 hereunder. The tests in Examples 1-6 werecarried out some months after the tests illustrated in Tables 1-7, witha better understanding of the invention, and led to improved results.

The invention will now be described, by way of non-limiting illustrativeexample, with reference to the following Examples 4-6, and withreference to the accompanying Tables 17-21.

In the Tables:

Table 17 shows shear strengths (MPa) against sample number forpolypropylene pipe samples having a reinforced polyesterresin-impregnated glass fibrous material applied by filament windingaccording to the process of the invention, with reference to therequired shear strength according to British Standard B.S. 6464;

Table 18 shows shear strengths (MPa) against sample number forpolypropylene pipe samples having a reinforcement of polyesterresin-impregnated glass fibrous material applied by tape wrappingaccording to the process of the invention, with reference to therequired shear strength according to British Standard B.S. 6464;

Table 19 shows shear strengths (MPa) against sample number forpolypropylene and high density polyethylene pipe samples having areinforcement of polyester resin-impregnated glass fibrous materialapplied by tape wrapping according to the process of the invention, withreference to the required shear strength according to British StandardB.S. 6464;

Table 20 shows shear strengths (MPa) against sample number for highdensity polyethylene pipe samples having a reinforcement of polyesterresin-impregnated fibrous material applied by tape wrapping according tothe invention, with reference to the required shear strength accordingto British Standard B.S. 6464;

Table 21 shows shear strengths (MPa) against sample number forpolypropylene pipe samples having a reinforcement of polyesterresin-impregnated fibrous material applied by hand lamination accordingto the invention, with reference to the required shear strengthaccording to British Standard B.S. 6464; and

Table 22 shows shear strengths (MPa) against sample number for highdensity polyethylene pipe samples having a reinforcement of epoxyresin-impregnated fibrous material applied by filament winding accordingto the invention, with reference to the required shear strengthaccording to British Standard B.S. 6464.

The fluorination of the pipes was carried out batchwise in an 11 m³ mildsteel reactor. Pipes were placed in the reactor and the reactor wasevacuated to an absolute pressure of 10 kPa. Then a F₂ /N₂ mixturecomprising 20% by volume F₂ was bled into the reactor to a totalpressure of 30 kPa. The fluorination was carried out at room temperaturefor 30 minutes, after which the reactor was evacuated and the pipesremoved.

For Example 1, six polypropylene pipes were used. The polypropylenematerial was PPH2222. The pipes were all 110 mm OD Class 10 pipinghaving a wall thickness of 8.5 mm. None of the pipes was degreasedbefore fluorination. Pipe numbers PP 1-PP4 were degreased with MEK andpipe numbers PP5 and PP6 were degreased with acetone after fluorinationand before reinforcement was applied. The reinforcing technique used wasfilament winding. The primary aim of Example 1 was to evaluate resinsfor adhesion of fibrous reinforcing to the pipes. On all the pipes thisresin was left to gel before the layers of resin-impregnatedreinforcement were applied.

For Example 2, four polypropylene pipes were used. The polypropylenematerial was PPH2222. The pipes were all 90 mm OD Class 10 piping havinga wall thickness of 7.0 mm. None of the pipes was clegreased beforefluorination. All the pipes were degreased with MEK after fluorinationand before reinforcement was applied. The reinforcing technique used wastape wrapping. The primary aim of Example 2 was to do repeatabilitytests on CRYSTIC 600 as a resin for adhesion of reinforcement to thepipes. This resin was left to gel before layers of the resin-impregnatedfibrous reinforcement were applied.

For Example 3, four polypropylene and four high density polyethylenepipes were used, whose polypropylene material and polyethylene materialwere respectively PPH2222 and GM5010. The polypropylene pipes were all110 mm OD class 10 piping having a wall thickness of 8.5 nm. All thepolypropylene pipes were degreased with MEK before fluorination. Of thepolypropylene pipes, pipe numbers PP 1 and PP2 were degreased with MEK(and pipe numbers PP3 and PP4 were not degreased), after fluorinationand beft)re the resin-impregnated fibrous reinforcement was applied.Similar degreasing was applied to the high density polyethylene pipes.The reinforcing technique was tape wrapping. The primary aim of Example3 was to do repeatability tests on CRYSTIC 600 as the resin for adhesionof the fibrous reinforcement to the pipes, to evaluate degreasing (andno degreasing) after fluorination and before the resin-impregnatedreinforcement was applied, to evaluate an alternative samplingtechnique. On all the pipes the resin used for adhesion of thereinforcement, and the reinforcement, were applied more or lesssimultaneously. In other words, the resin applied to the pipe surfacewas not left to gel before the resin-impregnated fibrous reinforcinglayers were applied.

For Example 4, four high density polyethylene pipes were used, thematerial being GM5010. The pipes were all 90 mm OC class 12 pipinghaving a wall thickness of 10.5 mm. All the pipes were degreased withMEK before fluorination. All the pipes were subjected to a proprietarytreatment after fluorination whereby the pipe surfaces were wiped with5% aqueous HCl solution, using Kimwipe paper, being then rinsed withdemineralized water and left to dry. None of the pipes was subjected toany other degreasing after fluorination before reinforcement wasapplied. The reinforcing technique used was tape wrapping. The primaryaim for Example 4 was to evaluate other resins instead of CRYSTIC 600for adhesion to the pipe of the fibrous reinforcement. On all the pipesthe resin applied to the pipe surface, and the reinforcing layers, wereapplied simultaneously, before any gelling of the adhesive resin appliedto the pipe surface.

For Example 5, two polypropylene pipes were used, the material beingPPH2222. The pipes were 50 mm OD class 10 piping having a wall thicknessof 40 mm. All the pipes were degreased with MEK before fluorination.None of the pipes was degreased after fluorination and before fibrousreinforcement was applied. The reinforcing technique used was handlamination. The primary aim for Example 5 was to evaluate CRYSTIC 392 asa resin applied to the pipes for adhesion of the fibrous reinforcementto the pipes. On all the pipes this resin was applied as a coating andleft to cure before the layers of resin-impregnated fibrousreinforcement were applied.

For Example 6, one high density polyethylene pipe was used, the materialbeing GM5010. The pipe was of 160 mm (OD class 10 piping having a wallthickness of 15.0 mm. The pipe was degreased neither before fluorinationnor after fluorination and before reinforcement was applied. Thereinforcing technique used was filament winding. The primary aim forExample 6 was to evaluate PRO-STRUCT 7907 as a resin for adhesion ofreinforcement to the pipe and PRO-STRUCT 988 as a resin for Impregnatingthe reinforcement. The PRO-STRUCT 7907 was applied as a coating and leftto gel before the layers of resin-impregnated fibrous reinforcement wereapplied.

Pipe samples were cut from the midpoint outwards and numbered asfollows:

    ______________________________________                                        7     5       3     1      2   4       6   8                                  ______________________________________                                    

Two testing techniques were used ie a standard and an alternativetechnique. In the standard technique a 20 mm length of the HDPE or PPwas machined out of a 60 mm length of pipe sample for the purposes ofliner push-out tests. In the alternative technique 20 mm lengths of pipesamples were cut and no HDPE or PP was machined out. Tooling wasdesigned appropriately for the purpose of liner push-out tests.

The push-out tests involved the pushing of the HDPE liner or the PPliner of each test piece, out of the reinforcing, and the measuring theforce required to do so. The shear strength or `push-out` strength wasthen calculated as follows:

    Shear strength (MPa)=F/π.d.l

where

F=maximum force required to shear the pipe from the overwrapping (N)

d=pipe outer diameter (mm)

l=liner push-out length (mm)

Results for Examples 1-6 are set forth respectively in Tables 17-22hereunder.

EXAMPLE 1

                                      TABLE 17                                    __________________________________________________________________________    Test Results                                                                                          Push        Average                                              Impreg-   Pipe                                                                             out Failure                                                                           Shear                                                                             of                                        Pipe number                                                                         Adhesion                                                                           nation                                                                             Sample                                                                             OD length                                                                            load                                                                              Stress                                                                            samples                                   (Material)                                                                          resin                                                                              resin                                                                              Number                                                                             (mm)                                                                             (mm)                                                                              (tonnes)                                                                          (MPa)                                                                             (MPa)                                     __________________________________________________________________________    PP1   Dion Dion 9100                                                                          PP1/1                                                                              110                                                                              20.0                                                                              5.75                                                                              8.2 8.78                                      (Poly-prop)                                                                         9100      PP1/2                                                                              110                                                                              20.0                                                                              6.14                                                                              8.7                                                           PP1/3                                                                              110                                                                              20.0                                                                              6.40                                                                              9.1                                                           PP1/4                                                                              110                                                                              20.0                                                                              6.50                                                                              9.2                                                           PP1/5                                                                              110                                                                              20.0                                                                              5.82                                                                              8.3                                                           PP1/6                                                                              110                                                                              20.0                                                                              6.50                                                                              9.2                                           PP2   Crystic                                                                            Crystic                                                                            PP2/1                                                                              110                                                                              20.0                                                                              7.15                                                                              10.1                                                                              9.10                                      (Poly-prop)                                                                         600  600  PP2/2                                                                              110                                                                              20.0                                                                              6.00                                                                              8.5                                                           PP2/3                                                                              110                                                                              20.0                                                                              6.22                                                                              8.8                                                           PP2/4                                                                              110                                                                              20.0                                                                              6.41                                                                              9.1                                                           PP2/5                                                                              110                                                                              20.0                                                                              6.70                                                                              9.5                                                           PP2/6                                                                              110                                                                              20.0                                                                              6.00                                                                              8.5                                           PP3   Dera-kane                                                                          Derakane                                                                           PP3/1                                                                              110                                                                              20.0                                                                              4.88                                                                              6.9 8.49                                      (Poly-prop)                                                                         470  411  PP3/2                                                                              110                                                                              20.0                                                                              5.80                                                                              8.2                                                           PP3/3                                                                              110                                                                              20.0                                                                              4.55                                                                              6.5                                                           PP3/4                                                                              110                                                                              20.0                                                                              6.80                                                                              9.7                                                           PP3/5                                                                              110                                                                              20.0                                                                              7.37                                                                              10.5                                                          PP3/6                                                                              110                                                                              20.0                                                                              6.50                                                                              9.2                                           PP4 (Poly-                                                                          Dera-kane                                                                          Derakane                                                                           PP4/1                                                                              110                                                                              20.0                                                                              5.48                                                                              7.8 7.50                                      prop) 8084 411  PP4/2                                                                              110                                                                              20.0                                                                              6.00                                                                              8.5                                                           PP4/3                                                                              110                                                                              20.0                                                                              4.44                                                                              6.3                                                           PP4/4                                                                              110                                                                              20.0                                                                              5.74                                                                              8.1                                                           PP4/5                                                                              110                                                                              20.0                                                                              4.88                                                                              6.9                                                           PP4/6                                                                              110                                                                              20.0                                                                              5.15                                                                              7.3                                           PP5   Dion Crystic                                                                            PP5/1                                                                              110                                                                              20.0                                                                              3.30                                                                              4.7 5.22                                      (Poly-prop)                                                                         9100 600  PP5/2                                                                              110                                                                              20.0                                                                              2.90                                                                              4.1                                                           PP5/3                                                                              110                                                                              20.0                                                                              2.42                                                                              3.4                                                           PP5/4                                                                              110                                                                              20.0                                                                              4.90                                                                              7.0                                                           PP5/5                                                                              110                                                                              20.0                                                                              4.89                                                                              6.9                                                           PP5/6                                                                              110                                                                              20.0                                                                              3.66                                                                              5.2                                           PP6   Primer +                                                                           Crystic                                                                            PP6/1                                                                              110                                                                              20.0                                                                              5.00                                                                              7.1 8.21                                      (Poly-prop)                                                                         Crystic                                                                            600  PP6/2                                                                              110                                                                              20.0                                                                              5.80                                                                              8.2                                                 600       PP6/3                                                                              110                                                                              20.0                                                                              5.45                                                                              7.7                                                           PP6/4                                                                              110                                                                              20.0                                                                              6.40                                                                              9.1                                                           PP6/5                                                                              110                                                                              20.0                                                                              5.65                                                                              8.0                                                           PP6/6                                                                              110                                                                              20.0                                                                              6.41                                                                              9.1                                           __________________________________________________________________________

EXAMPLE 2

                                      TABLE 18                                    __________________________________________________________________________    Test Results                                                                                         Push        Average                                    Pipe      Impreg-   Pipe                                                                             out Failure                                                                           Shear                                                                             of                                         number                                                                             Adhesion                                                                           nation                                                                             Sample                                                                             OD length                                                                            load                                                                              stress                                                                            samples                                    (material)                                                                         resin                                                                              resin                                                                              number                                                                             (mm)                                                                             (mm)                                                                              (kN)                                                                              (Mpa)                                                                             (Mpa)                                      __________________________________________________________________________    PP1  Crystic                                                                            Crystic                                                                            PP1/1                                                                              90 20.0                                                                              13.69                                                                             2.4                                                                              9.82                                        (polyprop)                                                                         600  600  PP1/2                                                                              90 20.0                                                                              19.38                                                                             3.4                                                           PP1/3                                                                              90 20.0                                                                              69.38                                                                             12.3                                                          PP1/4                                                                              90 20.0                                                                              65.96                                                                             11.7                                                          PP1/5                                                                              90 20.0                                                                              64.74                                                                             11.4                                                          PP1/6                                                                              90 20.0                                                                              70.50                                                                             12.5                                                          PP1/7                                                                              90 20.0                                                                              68.63                                                                             12.1                                                          PP1/8                                                                              90 20.0                                                                              72.06                                                                             12.7                                           PP2  Crystic                                                                            Crystic                                                                            PP2/1                                                                              90 20.0                                                                              9.69                                                                              1.7                                                                              9.64                                        (polyprop)                                                                         600  600  PP2/2                                                                              90 20.0                                                                              57.41                                                                             10.2                                                          PP2/3                                                                              90 20.0                                                                              56.70                                                                             10.0                                                          PP2/4                                                                              90 20.0                                                                              58.27                                                                             10.3                                                          PP2/5                                                                              90 20.0                                                                              61.31                                                                             10.8                                                          PP2/6                                                                              90 20.0                                                                              65.36                                                                             11.6                                                          PP2/7                                                                              90 20.0                                                                              60.38                                                                             10.7                                                          PP2/8                                                                              90 20.0                                                                              66.97                                                                             11.8                                           PP3  Crystic                                                                            Crystic                                                                            PP3/1                                                                              90 20.0                                                                              61.60                                                                             10.9                                                                             10.63                                       (Polyprop)                                                                         600  600  PP3/2                                                                              90 20.0                                                                              67.04                                                                             11.9                                                          PP3/3                                                                              90 20.0                                                                              69.09                                                                             12.2                                                          PP3/4                                                                              90 20.0                                                                              60.70                                                                             10.7                                                          PP3/5                                                                              90 20.0                                                                              57.80                                                                             10.2                                                          PP3/6                                                                              90 20.0                                                                              64.40                                                                             11.4                                                          PP3/7                                                                              90 20.0                                                                              63.70                                                                             11.3                                                          PP3/8                                                                              90 20.0                                                                              36.28                                                                             6.4                                            PP4  Crystic                                                                            Crystic                                                                            PP4/1                                                                              90 20.0                                                                              11.48                                                                             2.0                                                                              7.60                                        (Polyprop)                                                                         600  600  PP4/2                                                                              90 20.0                                                                              46.87                                                                             8.3                                                           PP4/3                                                                              90 20.0                                                                              14.36                                                                             2.5                                                           PP4/4                                                                              90 20.0                                                                              63.91                                                                             11.3                                                          PP4/5                                                                              90 20.0                                                                              63.65                                                                             11.3                                                          PP4/6                                                                              90 20.0                                                                              5.85                                                                              1.0                                                           PP4/7                                                                              90 20.0                                                                              69.43                                                                             12.3                                                          PP4/8                                                                              90 20.0                                                                              68.11                                                                             12.0                                           __________________________________________________________________________

EXAMPLE 3

                                      TABLE 19                                    __________________________________________________________________________                  Test Results            Test Results (Alternative Sampling                                            Technique)                                                    Push        Average     Push                            Pipe      Impreg-     out Failure                                                                           Shear                                                                             of      Pipe                                                                              out Failure                                                                           Shear                   number                                                                             Adhesion                                                                           nation                                                                            Sample                                                                            Pipe Od                                                                           length                                                                            load                                                                              stress                                                                            samples                                                                           Sample                                                                            OD  length                                                                            load                                                                              stress                  (material)                                                                         resin                                                                              resin                                                                             number                                                                            (mm)                                                                              (mm)                                                                              (kN)                                                                              (Mpa)                                                                             (Mpa)                                                                             number                                                                            (mm)                                                                              (mm)                                                                              (kN)                                                                              (Mpa)                   __________________________________________________________________________    PP1  Crystic                                                                            Crystic                                                                           PP1/1                                                                             110 20.0                                                                              57.07                                                                             8.3 7.77                                                                              PP1/A                                                                             110 20  92.46                                                                             13.4                    (Polyprop)                                                                         600  600 PP1/2                                                                             110 20.0                                                                              48.25                                                                             7.0     PP1/B                                                                             110 20  90.06                                                                             13.0                                  PP1/3                                                                             110 20.0                                                                              72.13                                                                             10.4                                                          PP1/4                                                                             110 20.0                                                                              52.14                                                                             7.5                                                           PP1/5                                                                             110 20.0                                                                              64.30                                                                             9.3                                                           PP1/6                                                                             110 20.0                                                                              35.37                                                                             5.1                                                           PP1/7                                                                             110 20.0                                                                              63.12                                                                             9.1                                                           PP1/8                                                                             110 20.0                                                                              37.31                                                                             5.4                                             PP2  Crystic                                                                            Crystic                                                                           PP2/1                                                                             110 20.0                                                                              73.13                                                                             10.6                                                                              11.04                                                                             PP2/A                                                                             110 20  93.04                                                                             13.5                    (Polyprop)                                                                         600  600 PP2/2                                                                             110 20.0                                                                              82.53                                                                             11.9    PP2/B                                                                             110 20  99.56                                                                             14.4                                  PP2/3                                                                             110 20.0                                                                              64.00                                                                             9.3                                                           PP2/4                                                                             110 20.0                                                                              86.71                                                                             12.5                                                          PP2/5                                                                             110 20.0                                                                              59.85                                                                             8.7                                                           PP2/6                                                                             110 20.0                                                                              87.66                                                                             12.7                                                          PP2/7                                                                             110 20.0                                                                              73.32                                                                             10.6                                                          PP2/8                                                                             110 20.0                                                                              83.26                                                                             12.0                                            PP3  Crystic                                                                            Crystic                                                                           PP3/1                                                                             110 20.0                                                                              41.81                                                                             6.0 8.55                                                                              PP3/A                                                                             110 20  97.54                                                                             14.1                    (Polyprop)                                                                         600  600 PP3/2                                                                             110 20.0                                                                              59.45                                                                             8.6     PP3/B                                                                             110 20  97.17                                                                             14.1                                  PP3/3                                                                             110 20.0                                                                              51.23                                                                             7.4                                                           PP3/4                                                                             110 20.0                                                                              67.55                                                                             9.8                                                           PP3/5                                                                             110 20.0                                                                              69.78                                                                             10.1                                                          PP3/6                                                                             110 20.0                                                                              49.50                                                                             7.2                                                           PP3/7                                                                             110 20.0                                                                              64.21                                                                             9.3                                                           PP3/8                                                                             110 20.0                                                                              69.20                                                                             10.0                                            PP4  Crystic                                                                            Crystic                                                                           PP4/1                                                                             110 20.0                                                                              58.81                                                                             8.5 10.32                                                                             PP7/A                                                                             110 20  65.46                                                                             9.5                     (Polyprop)                                                                         600  600 PP4/2                                                                             110 20.0                                                                              78.85                                                                             11.4    PP7/B                                                                             110 20  96.69                                                                             14.0                                  PP4/3                                                                             110 20.0                                                                              77.32                                                                             11.2                                                          PP4/4                                                                             110 20.0                                                                              70.94                                                                             10.3                                                          PP4/5                                                                             110 20.0                                                                              75.52                                                                             10.9                                                          PP4/6                                                                             110 20.0                                                                              63.64                                                                             9.2                                                           PP4/7                                                                             110 20.0                                                                              74.11                                                                             10.7                                            PE1  Crystic                                                                            Crystic                                                                           PE1/1                                                                             110 20.0                                                                              75.53                                                                             10.9                                                                              10.11                                                                             PE1/A                                                                             110 20  88.42                                                                             12.8                    (Poly-                                                                             600  600 PE1/2                                                                             110 20.0                                                                              68.42                                                                             9.9     PE1/B                                                                             110 20  86.10                                                                             12.5                    ethylene)     PE1/3                                                                             110 20.0                                                                              76.92                                                                             11.1                                                          PE1/4                                                                             110 20.0                                                                              74.93                                                                             10.8                                                          PE1/5                                                                             110 20.0                                                                              52.88                                                                             7.7                                                           PE1/6                                                                             110 20.0                                                                              73.75                                                                             10.7                                                          PE1/7                                                                             110 20.0                                                                              S8.62                                                                             6.5                                                           PE1/8                                                                             110 20.0                                                                              77.84                                                                             11.3                                            PE2  Crystic                                                                            Crystic                                                                           PE2/1                                                                             110 20.0                                                                              74.08                                                                             10.7                                                                              10.02                                                                             PE2/A                                                                             110 20  94.63                                                                             13.7                    (Poly-                                                                             600  600 PE2/2                                                                             110 20.0                                                                              72.89                                                                             10.5    PE2/B                                                                             110 20  90.22                                                                             13.1                    ethylene)     PE2/3                                                                             110 20.0                                                                              76.71                                                                             11.1                                                          PE2/4                                                                             110 20.0                                                                              78.48                                                                             11.4                                                          PE2/5                                                                             110 20.0                                                                              75.61                                                                             10.9                                                          PE2/6                                                                             110 20.0                                                                              69.55                                                                             10.1                                                          PE2/7                                                                             110 20.0                                                                              74.81                                                                             10.8                                                          PE2/8                                                                             110 20.0                                                                              75.91                                                                             11.0                                            PE3  Crystic                                                                            Crystic                                                                           PE3/1                                                                             110 20.0                                                                              42.89                                                                             6.2 7.82                                                                              PE3/A                                                                             110 20  73.36                                                                             10.6                    (Poly-                                                                             600  600 PE3/2                                                                             110 20.0                                                                              46.47                                                                             6.7     PE3/B                                                                             110 20  64.74                                                                             9.4                     ethylene)     PE3/3                                                                             110 20.0                                                                              46.60                                                                             6.7                                                           PE3/4                                                                             110 20.0                                                                              51.42                                                                             7.4                                                           PE3/5                                                                             110 20.0                                                                              61.72                                                                             8.9                                                           PE3/6                                                                             110 20.0                                                                              58.73                                                                             8.5                                                           PE3/7                                                                             110 20.0                                                                              67.53                                                                             9.8                                                           PE3/8                                                                             110 20.0                                                                              56.92                                                                             8.2                                             PE4  Crystic                                                                            Crystic                                                                           PE4/1                                                                             110 20.0                                                                              18.35                                                                             2.7 5.32                                                                              PE4/A                                                                             110 20  67.53                                                                             9.8                     (Poly-                                                                             600  600 PE4/2                                                                             110 20.0                                                                              39.39                                                                             5.7     PE4/B                                                                             110 20  65.65                                                                             9.5                     ethylene)     PE4/3                                                                             110 20.0                                                                              33.72                                                                             4.9                                                           PE4/4                                                                             110 20.0                                                                              63.04                                                                             9.1                                                           PE4/5                                                                             110 20.0                                                                              10.24                                                                             1.5                                                           PE4/6                                                                             110 20.0                                                                              48.05                                                                             7.0                                                           PE4/7                                                                             110 20.0                                                                              20.96                                                                             3.0                                                           PE4/8                                                                             110 20.0                                                                              60.39                                                                             8.7                                             __________________________________________________________________________

EXAMPLE 4

                                      TABLE 20                                    __________________________________________________________________________                       TEST RESULTS (ALTERNATIVE                                                     SAMPLING TECHNIQUE)                                        TEST RESULTS               Push                                                             Impreg-  Pipe                                                                              out Failure                                                                           Shear                                      Pipe Number   nation                                                                             Sample                                                                            OD  length                                                                            load                                                                              Stress                                     (Material)                                                                           Adhesion resin                                                                       resin                                                                              number                                                                            (mm)                                                                              (mm)                                                                              (kN)                                                                              (Mpa)                                      __________________________________________________________________________    PE1    Crystic 600                                                                          Crystic                                                                            PE1/A                                                                             90  20  57.78                                                                             10.2                                       Standard wall                                                                        NCS    600 NCS                                                                            PE1/B                                                                             90  20  60.54                                                                             10.7                                       thickness                                                                     (Polyethylene)                                                                PE2    Crystic 600SB                                                                        Crystic                                                                            PE2/A                                                                             90  20  69.58                                                                             12.3                                       Standard wall 600SB                                                                              PE2/B                                                                             90  20  63.12                                                                             11.2                                       thickness                                                                     (Polyethylene)                                                                PE3    Dion 6694                                                                            Dion PE3/A                                                                             90  20  56.89                                                                             10.1                                       Standard wall 6694 PE3/B                                                                             90  20  53.89                                                                             9.5                                        thickness                                                                     (Polyethylene)                                                                PE4    Crystic 392                                                                          Crystic                                                                            PE4/A                                                                             90  20  66.66                                                                             11.8                                       Standard wall 392  PE4/B                                                                             90  20  64.03                                                                             11.3                                       thickness                                                                     (Polyethylene)                                                                __________________________________________________________________________

EXAMPLE 5

                                      TABLE 21                                    __________________________________________________________________________    TEST RESULTS                                                                                          Push        Average                                                       Pipe                                                                              out Failure                                                                           Shear                                                                             of                                        Pipe Adhesion                                                                           Impregnation                                                                        Sample                                                                            OD  length                                                                            load                                                                              Stress                                                                            samples                                   number                                                                             resin                                                                              resin number                                                                            (mm)                                                                              (mm)                                                                              (kN)                                                                              (Mpa)                                                                             (Mpa)                                     __________________________________________________________________________    PP1  Crystic                                                                            Derakane                                                                            PP1/1                                                                             50  20.0                                                                              31.59                                                                             10.1                                                                              9.98                                      (Polyprop)                                                                         392  411   PP1/2                                                                             50  20.0                                                                              30.12                                                                             9.6                                                           PP1/3                                                                             50  20.0                                                                              31.54                                                                             10.0                                                          PP1/4                                                                             50  20.0                                                                              31.49                                                                             10.0                                                          PP1/5                                                                             50  20.0                                                                              32.00                                                                             10.2                                          PP2  Crystic                                                                            Derakane                                                                            PP2/1                                                                             50  20.0                                                                              28.66                                                                             9.1 9.86                                      (Polyprop)                                                                         392  411   PP2/2                                                                             50  20.0                                                                              31.99                                                                             10.2                                                          PP2/3                                                                             50  20.0                                                                              32.43                                                                             10.3                                                          PP2/4                                                                             50  20.0                                                                              30.16                                                                             9.6                                                           PP2/5                                                                             50  20.0                                                                              31.64                                                                             10.1                                          __________________________________________________________________________

EXAMPLE 6

                                      TABLE 22                                    __________________________________________________________________________    Test Results                                                                                          Push        Average                                   Pipe                 Pipe                                                                             out Failure                                                                           Shear                                                                             of                                        number                                                                             Adhesion                                                                           Impregnation                                                                        Sample                                                                             OD length                                                                            load                                                                              Stress                                                                            samples                                   (Material)                                                                         resin                                                                              resin number                                                                             (mm)                                                                             (mm)                                                                              (kN)                                                                              (Mpa)                                                                             (Mpa)                                     __________________________________________________________________________    PE1  Pro-Struct                                                                         Pro-Struct                                                                          PE1/1                                                                              160                                                                              10.36                                                                             40.28                                                                             7.7 9.06                                      (Polyethyl                                                                         7909 988   PE1/2                                                                              160                                                                              13.53                                                                             44.88                                                                             6.6                                           ene)            PE1/3                                                                              160                                                                              13.54                                                                             70.17                                                                             10.3                                                          PE1/4                                                                              160                                                                              14.86                                                                             67.23                                                                             9.0                                                           PE1/5                                                                              160                                                                              12.04                                                                             65.17                                                                             10.8                                                          PE1/6                                                                              160                                                                              15.33                                                                             76.64                                                                             9.9                                           __________________________________________________________________________

It is an advantage of the invention that it permits polyolefin pipes andtanks to be strengthened or reinforced by a resin-impregnated fibrouswrapping material. As the bond between the resin and the surfaceactivated pipe or tank is believed to be a chemical bond, the process isless labour intensive than similar processes in which the bond is amechanical bond. As a result, the pipes or tanks, eg glass fibrereinforced PP pipes or tanks, can be manufactured at lower cost.

We claim:
 1. In the production of a component of a plastics material which is strengthened and reinforced by a fibrous material which has been impregnated with a resin which adheres to a surface of the component, by contacting said surface of the component with said fibrous material impregnated with the resin in a settable state, and effecting setting of the resin to cause said resin-impregnated fibrous material to adhere to said surface of the component, the process which comprises using as the plastics material a polyolefin material and which includes the step, prior to the contacting, of subjecting said surface of the component to activation thereof, the activation being by surface fluorination in the form of oxyfluorination by exposing the surface of the component to an activating gas consisting essentially of molecules and comprising fluorine-containing molecules and oxygen-containing molecules at a pressure of 1-500 kPa, the gas being at a temperature of above 0° C., the plastics material of the component having a melting point above said gas temperature and the oxyfluorination acting to incorporate fluorine-containing substituents and oxygen-containing substituents, derived from molecules of the activating gas, into the surface of the component.
 2. A process as claimed in claim 1, in which the polyolefin material is selected from the group consisting of polyethylenes, polypropylenes, copolymers of ethylene and propylene and blends of such polymers.
 3. A process as claimed in claim 1, in which the surface activation acts to provide the surface-activated component with a surface tension at 20° C. of at least 40 mN/m.
 4. A process as claimed in claim 1, in which the activating gas comprises a fluorine-containing gas which forms part of a gas mixture with other gases, the fluorine-containing gas forming 1-30% by volume of said gas mixture and the temperature of the gas mixture being 20-100° C.
 5. A process as claimed in claim 4, in which the gas mixture comprises 5-20% by volume of the fluorine-containing gas and 5-95% by volume of oxygen.
 6. A process as claimed in claim 5, in which, after said oxyfluorination, the surface is subjected to hydrolysis.
 7. A process as claimed in claim 1, in which the fibrous material is subjected to surface fluorination thereof prior to impregnation thereof with resin.
 8. A process as claimed in claim 7, in which the fibrous material has fibres which are selected from the group consisting of polyester fibres, polyamide fibres, polyolefin fibres and mixtures thereof.
 9. A process as claimed in claim 1, in which the surface is subjected to degreasing prior to said activation thereof.
 10. A process as claimed in claim 1, in which the surface, after said activation thereof and prior to the contacting, is subjected to degreasing.
 11. A process as claimed in claim 1, in which causing the fibrous material to adhere to the surface of the component is by means of a resin which is different from the resin which impregnates the fibrous material, each resin being selected from epoxy resins and polyester resins.
 12. A process as claimed in claim 1, in which causing the fibrous material to adhere to the surface of the component is by means of a resin which is the same as the resin which impregnates the fibrous material, each resin being selected from epoxy resins and polyester resins.
 13. A component of a plastics material which is strengthened and reinforced by a resin-impregnated fibrous material which adheres to a surface of the component, produced in accordance with the process of claim
 1. 